The present invention relates to control apparatuses for automatic transmissions that are mounted on vehicles and the like. More particularly, the present invention relates to control apparatuses for automatic transmissions, which determine whether a failure has occurred or not (hereinafter sometimes referred to as a “failure determination”) based on the gear ratio, after a shifting operation is performed by changing the engagement/disengagement states of a plurality of friction engagement elements.
In multistage automatic transmissions that are mounted on, e.g., vehicles, a shifting operation is performed by changing the engagement/disengagement state of friction engagement elements such as clutches and brakes. Incidentally, in the above shifting operation for changing the engagement/disengagement states of friction engagement elements, engagement and disengagement of the friction engagement elements are controlled by electrically controlling, e.g., linear solenoid valves in a hydraulic control apparatus. However, there is a possibility that an engagement failure or a disengagement failure occurs for some reason. As used herein, the engagement failure is a failure in which a friction engagement element, which is supposed to be disengaged, is in an engaged state, and the disengagement failure is a failure in which a friction engagement element, which is supposed to be engaged, is in a disengaged state. If such a failure occurs, a failsafe operation needs to be performed according to the failure determination in order to ensure traveling safety. Thus, a shift control apparatus, which makes a failure determination by comparing a gear ratio during a shifting operation (a gear ratio) with a predetermined threshold value, has been proposed (see Japanese Patent Application Publication No. JP-A-2007-255518).